During the manufacturing of metal containers used in the beverage and food industry, certain coatings are often applied to internal and external surfaces of the containers. These organic and inorganic chemical coatings are applied to prevent cans from staining during retorting and other processes, as well as to prevent corrosion and “scalping”, which is the alteration of the taste of a beverage or food stored in a container resulting from the beverage or food contacting the interior surface of the container.
One particular use of coatings involves the use of a “conversion coating”, which is typically a zirconium-phosphate coating that is applied to the exterior of a container to prevent staining of the container exterior during retort operations. As described herein, “retort” refers to any operation wherein a beverage or food container is heated beyond 200° F., and more typically between about 250-300° F., and which typically includes exposing the container to steam or hot water having a pH equal to or greater than 7.0, i.e. basic.
Although the conversion coating provides significant advantages when applied to an exterior lower portion, or dome of the container, it has the adverse effect of causing ink and decorative coating adhesion loss on the “neck” or upper portion of containers during manufacturing and retort operations. Hence, the container becomes unfit for its intended purpose and is subsequently discarded, which is both time consuming, expensive, and disruptive to a manufacturing operation. As appreciated by one skilled in the art, in modern can manufacturing facilities with the capability of producing over 20 million containers a day any loss in production is disruptive and expensive.
Thus, there is a significant need in the container industry for a method and apparatus for removing a conversion coating or other similar coating from a predetermined portion of a container, while retaining the coating on another portion of the container. Furthermore, as appreciated by one skilled in the art, the invention is not limited to the selective removal of coatings from containers, but rather may be used in any type of operation when a selective portion of a coating is desired to be applied or removed from a surface or portion of an apparatus. The following disclosure describes an improved apparatus and method for efficiently removing a predetermined amount of conversion coating deposited on a container during production.